Fabrication of Bi-Te Based Thermoelectric Semiconductors by Using Hybrid Powders

摘要:

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P-type Bi0.5Sb1.5Te3 compounds doped with 3wt% Te were fabricated by spark plasma sintering and their mechanical and thermoelectric properties were investigated. The sintered compounds with the bending strength of more than 50MPa and the figure-of-merit 2.9×10-3/K were obtained by controlling the mixing ratio of large powders (PL) and small powders (PS). Compared with the conventionally prepared single crystal thermoelectric materials, the bending strength was increased up to more than three times and the figure-of-merit Z was similar those of single crystals. It is expected that the mechanical properties could be improved by using hybrid powders without degradation of thermoelectric properties.

摘要: When a bicrystal or polycrystal are subjected to a change in temperature, the individual responses of the two adjoining crystals may differ in a manner, which tends to produce a dilatational mismatch along grain boundaries. If compatibility is to be retained along the interface, an additional set of stresses must then be generated in order to conserve this compatibility. ‘Compatibility stresses’ will also be generated whenever a polycrystal is heated or cooled and the thermal expansion coefficients of the individual grains are different due to thermal expansion anisotropy. In such cases adjacent grains will attempt to change dimensions and develop mismatches by amounts controlled by the parameter Δa*ΔΤ, where Δa is the difference between the thermal expansion coefficients in the appropriate directions, and ΔΤ is the temperature change. These ‘compatibility stresses’ may be relieves if grain boundary motion, triple junction migration and grain growth are possible. These ‘compatibility stresses’ may play important role in the kinetic
behavior of the microstructure ranging from influencing the behavior of lattice dislocations near the grain boundaries to promoting grain boundary and triple junction dragging or moving. The motion of the ‘special’ grain boundaries, triple junctions with ‘special’ grain boundaries and twins under the influence of internal mechanical stresses is the main subject of this paper.

摘要: Monodispersed Cu powders were prepared in aqueous solution through a wet-reduction
process with hydrazine hydrate (N2H4·H2O). In particular, the effect of the dispersant such as sodium
pyrophosphate decahydrate (Na4O7P2·10H2O), carboxymethyl cellulose sodium salt (CMC) in water
solvent on the particle size for the prepared Cu powders was investigated. The Cu powders essentially
were monodispersed and irregular in shape regardless of reaction temperature and dispersant. In the case
of adding the Na4O7P2·10H2O, the particle size of Cu powders increased with the increase of reaction
temperature, which the particles were agglomerated in irregular shape and became to be large. The
particle size distributions was asymmetry and to be broad regardless of reaction temperature. On the other
hand, when the CMC was added, the particle size of Cu powders, which were much finer compared with
adding the Na4O7P2·10H2O as a dispersant, was not much changed with reaction temperature. The particle
size distribution of Cu powder was much narrow regardless of reaction temperature. As a result, it would
be suggested that the CMC was more effective dispersant reagent to produce the monodispersed and fine
Cu powders with narrow size distribution using the wet chemical reduction process

摘要: With the development of high toughness pipeline, it is necessary to develop new welding
wires for high-efficiency submerged-arc welding, to produce weld metals whose properties can
match corresponding ones of the base metal, such as strength, toughness, H2S corrosion resistance,
etc. In this paper, the weld wires with variations of elements have been designed, and the effects of
alloy elements on the microstructures and low temperature impact toughness are discussed.

摘要: Porous calcia stabilized zirconia ceramics (CSZC) with closed pores were presurelessly sintered by adding different contents of zirconia hollow balls. CSZC FGM with porosity gradient structure was then fabricated by laminating five layers with designed contents of zirconia hollow balls. The porosity, microstructure, and bending strength of the obtained CSZC samples were characterized. The results show that the hollow balls distribute uniformly and are well bonded with the matrix, and the porous structure is mainly composed of closed pores. The porosity of the CSZC increases linearly from 5.7 % to 31.6 % when the content of zirconia hollow balls increases from 0 % to 30 %, and the bending strength decreases rapidly from 297 MPa to 30 MPa. The thermal shock behavior of the CSZC and FGM was evaluated using air-quenching technique. It is shown that the residual bending strength of the quenched samples increases after several quenching cycles, and the samples are damaged by thermal shock after eight thermal cycles because of the production of monoclinic zirconia. FGM samples with porosity gradient structure can endure above twelve thermal shock cycles and exhibits better thermal shock resistance.

摘要: Sodium hexatitanate (Na2O•6TiO2) whiskers with an average diameter and aspect ratio of 1-3 µm and 10-20 respectively were synthesized by calcinating mixtures of industrial grade sodium carbonate (Na2CO3), anatase TiO2 and potassium fluoride (KF). The growth of sodium hexatitanate whiskers was obtainable in a range of TiO2/Na2CO3 molar ratio from 4 to 6, heating temperature from 940 °C to 1000 °C and content of KF from 5 wt.% to 7 wt.% with different morphologies and aspect ratio of the products. The role of KF on the growth behavior of Na2O•6TiO2 whiskers was demonstrated by structural and morphological observation.